In recent years, communication traffic is constantly increasing along with the spread of broadband service and the increase in the utilization of information interchange by companies which take advantage of the internet, and demand for increase of the capacity and the rate of communication networks is unrelenting.
The wavelength division multiplexing (WDM) communication technique greatly increases the transmission capacity per one optical fiber, and has realized great capacity increase between two locations. However, when relaying the optical signal at a communication node, it is necessary to demultiplex the wavelength division multiplexed signals for each wavelength, and to route the data packets in each optical signal individually for each packet.
Nowadays, routing of data packets is performed electrically by converting the optical signal to an electrical signal, but, along with increases in the transmission rate and increases in capacity, the routing by electrical processing of a high volume signal will reach a limit in the near future.
As a means for solving this problem, wavelength path routing is proposed, in which the optical signals are not converted into electrical signals, but are routed in the optical state (upon the optical layer).
FIG. 25 is an optical communication network system based upon wavelength path routing which has been implemented using an arrayed-waveguide grating which is provided with a wavelength-routing function (for example, refer to “32×32 full-mesh (1024 path) wavelength-routing WDM network based upon uniform-loss cyclic-frequency arrayed-waveguide grating”, IEE Electron. Lett., vol. 36, no., pp. 1294-1295, 2000, by K. Kato et al.).
The optical communication network shown in FIG. 25 shows the case in which the number of the communication nodes is four, and 100-1 through 100-4 are communication nodes, 110 is a 4×4 arrayed-waveguide grating having four input ports and four output ports, 120-1 through 120-4 are upstream optical transmission lines along which pass optical signals which have been transmitted towards the arrayed-waveguide grating 110 from the communication nodes 100-1 through 100-4, and 130-1 through 130-4 are downstream optical transmission lines along which pass optical signals which have been transmitted from the arrayed-waveguide grating 110 towards the communication nodes 100-1 through 100-4.
The arrayed-waveguide grating 110 is an optical component which has input ports 140-1 through 140-4 and output ports 150-1 through 150-4, and the output ports 150-1 through 150-4 which output the optical signals which have been inputted to the input ports 140-1 through 140-4 are determined uniquely according to the wavelengths of these optical signals.
The upstream optical transmission lines 120-1 through 120-4 are respectively connected to the input ports 140-1 through 140-4 of the arrayed-waveguide grating 110, while the downstream transmission lines 130-1 through 130-4 are respectively connected to the output ports 150-1 through 150-4 of the arrayed-waveguide grating 110.
FIGS. 26 and 27 show how the input ports 140-1 through 140-4 and the output ports 150-1 through 150-4 of the 4×4 arrayed-waveguide grating 110, which has the four input ports 140-1 through 140-4 and the four output ports 150-1 through 150-4, are connected together according to wavelength.
FIG. 26 shows the case of a 4×4 arrayed-waveguide grating 110 which is provided with a cyclic-wavelength characteristic, and moreover FIG. 27 shows the case of one which is not provided with a cyclic-wavelength characteristic.
For example, in FIG. 26, when an optical signal of wavelength λ3 has been inputted to the input port 140-1, this optical signal of wavelength λ3 is outputted from the output port 150-3. Accordingly, when an optical signal of wavelength λ3 is transmitted from the communication node 100-1, this optical signal of wavelength λ3 is inputted to the input port 140-1 of the arrayed-waveguide grating 110 via the optical transmission line 120-1, and, due to wavelength-routing, this optical signal of wavelength λ3 is outputted from the output port 150-3 of the arrayed-waveguide grating 110. Subsequently, the optical signal of wavelength λ3 arrives at the communication node 100-3 along the optical transmission line 130-3. In this manner, it is possible to perform routing upon the optical layer based upon the wavelength of the optical signals by utilizing the wavelength-routing function of the arrayed-waveguide grating 110, and to perform communication between the communication nodes 100-1 through 100-4, without converting the optical signals into electrical signals.
Furthermore, an optical communication network having a structure as shown in FIG. 28 is known as a network system which is capable of answering to increase of transmission capacity by providing an optical path of two or more wavelengths between two communication nodes (refer to Japanese Unexamined Patent Application, First Publications Nos. 2000-134649, 2002-165238, and 2002-262319).
The optical communication network shown in FIG. 28 shows the case in which the number of communication nodes is four. In FIG. 28, 1200-1 through 1200-4 denote communication nodes, 1220-1 through 1220-4 denote wavelength-band demultiplexing devices, 1230-1 through 1230-4 denote wavelength-band multiplexing devices, and 1240 denotes an optical switch.
The communication nodes 1200-1 through 1200-4 wavelength division multiplex and output a plurality of optical signals. The optical signals which are outputted are inputted to the respective wavelength-band demultiplexing devices 1220-1 through 1220-4. These wavelength-band demultiplexing devices are provided with the function of distributing the wavelength division multiplexed signals which have been inputted to a plurality of output ports. At this time, the signals which are outputted from the respective output ports are wavelength division multiplexed for each combination of wavelengths which are determined in advance, in other words for each wavelength-band. The routes of the optical signals which are outputted from the wavelength-band demultiplexing devices are changed over by the optical switch 1240, and the outputs thereof are inputted to the wavelength-band multiplexing devices 1230-1 through 1230-4. These wavelength-band multiplexing devices, in a manner opposite to the wavelength-band demultiplexing devices, are provided with the function of bundling together signals which have been wavelength division multiplexed for each wavelength-band to a single output port. The signals which have been outputted from the wavelength-band multiplexing devices 1230-1 through 1230-4 are inputted to the communication nodes 1200-1 through 1200-4, and are received thereby.
Since it is possible to provide an optical path in this type of optical communication network between two communication nodes for each wavelength-band, accordingly it is possible to provide a plurality of optical paths between the communication nodes up to the number of wavelengths which are included within a wavelength-band.
It should be understood that, as shown in FIG. 29, there is also a known method of forming the optical switch 1240 by combining a plurality of small scale optical switches 1240-1 through 1240-3 (refer to Japanese Unexamined Patent Application, First Publication No. 2001-8244).
Moreover, it should be understood that there is known an optical communication network (refer to Japanese Unexamined Patent Application, First Publication No. 2002-300137) which utilizes the CWDM (Coarse WDM) standard having a grid of 20 nm interval in the wavelength-band demultiplexing devices or the wavelength-band multiplexing devices, and which forms wavelength-bands in which DWDM (Dense WDM) signals of 100 GHz (about 0.8 nm) intervals are accommodated in the 20 nm bands.
However, with the above-described conventional optical communication network system based upon wavelength-routing of the arrayed-waveguide grating 110, although the communication node 100-1 can transmit information to the communication node 100-3 with an optical signal of wavelength λ3, it is difficult to increase the transmission capacity from the communication node 100-1 to the communication node 100-3 above the transmission capacity of an optical signal of one wavelength.
In other words, it is only possible to establish a single optical path between two communication nodes with the conventional technique shown in FIG. 25. In this manner, with an optical communication network system of the conventional structure which is based upon wavelength-routing by an arrayed-waveguide grating 110, there is the problematical aspect that it is extremely difficult to increase the transmission capacity by increasing the number of optical paths between the communication nodes.
Furthermore, with the method of establishing an optical path between communication nodes for each wavelength-band, the number of communication nodes to which some communication node can transmit information is limited to the number of wavelength-bands, and there is the problem that, if the number of communication nodes exceeds the number of the wavelength-bands, then a combination of the communication nodes is created in which information is not delivered unless it is transmitted via other communication nodes.
On the other hand, FIG. 30 shows an example of a conventional optical cross connect device (refer to “Optical Networks”, R. Ramaswami, K. N. Sivarajan, Morgan Kaufman Publishers Inc., 1998, p. 341 etc.). In this figure, 1-1, 1-2, . . . 1-N are wavelength division demultiplexing circuits, 2-1, 2-2, . . . 2-N are wavelength division multiplexing circuits, 3-1, 3-2, . . . 3-m are optical matrix switches, 4-1, 4-2, . . . 4-N are input optical fibers (optical transmission lines upon the input side), and 5-1, 5-2, . . . 5-N are output optical fibers (optical transmission lines upon the output side).
The wavelength division demultiplexing circuits 1-1 through 1-N each have a single input port and m output ports, and the input port is connected via the input optical fibers 4-1 through 4-N to a certain single communication node (not shown in the figure), and a wavelength division multiplexed signal which has been inputted from the certain communication node to the input port is demultiplexed by wavelength and is outputted from the respective output ports.
The wavelength division multiplexing circuits 2-1 through 2-N each has m input ports and a single output port, and the output port is connected to a certain communication node (not shown in the figure) via output optical fibers 5-1 through 5-N, so that optical signals of a maximum of m wavelengths which have been inputted to the respective input ports are wavelength division multiplexed to form a wavelength division multiplexed signal, which is outputted from the output port to the certain communication node.
The optical matrix switches 3-1 through 3-m each has N input ports and N output ports, and each of the input ports is respectively connected to that output port, among the output ports of the wavelength division demultiplexing circuits 1-1 through 1-N, which outputs an optical signal of the same wavelength, while each of the output ports is separately connected to the input ports of the wavelength division multiplexing circuits 2-1 through 2-N.
With this type of optical cross connect device, the wavelength division multiplexed signals of m wavelengths which have been transmitted via the input optical fibers 4-1 through 4-N from the respective communication nodes are inputted to the wavelength division demultiplexing circuits 1-1 through 1-N, are demultiplexed by wavelength, are outputted from the separate output ports, and are respectively inputted by wavelength to the different optical matrix switches 3-1 through 3-m. Routes, that is, the wavelength division multiplexing circuits 2-1 through 2-N which are the output destination, are changed over so that the optical signals which have been inputted to the optical matrix switches 3-1 through 3-m are outputted to the desired output optical fibers 5-1 through 5-N under the condition that optical signals of the same wavelength are not outputted from the same output optical fiber, in other words, under the condition that optical signals of the same wavelength are not inputted to the same wavelength division multiplexing circuit, and the optical signals of m wavelengths which have been inputted to the wavelength division multiplexing circuits 2-1 through 2-N are wavelength division multiplexed, and are transmitted to the respective communication nodes via the output optical fibers 5-1 through 5-N.
With the circuit of FIG. 30, it is possible to establish settings so that all the optical signals of all the wavelengths which have been multiplexed upon the input optical fibers are outputted from the desired output optical fibers. However, due to the condition that optical signals of the same wavelength are not outputted from the same output optical fiber, the optical paths between the input optical fibers and the output optical fibers cannot be set freely.
For example, the case may be considered in which the number of the input optical fibers and the number of the output optical fibers are both 8, and the number of multiplexed wavelengths is 4. At this time, under the conditions that the optical paths between the input optical fibers and the output optical fibers are not arranged, that is, as shown in FIGS. 31A through 31D, optical paths which use the wavelength λ1 are established between the #1 input optical fiber and the #3 output optical fiber and between the #3 input optical fiber and the #1 output optical fiber, optical paths which use the wavelength λ2 are established between the #2 input optical fiber and the #5 output optical fiber and between the #5 input optical fiber and the #2 output optical fiber, optical paths which use the wavelength λ3 are established between the #2 input optical fiber and the #8 output optical fiber and between the #8 input optical fiber and the #2 output optical fiber; and optical paths which use the wavelength λ4 are established between the #1 input optical fiber and the #3 output optical fiber and between the #3 input optical fiber and the #1 output optical fiber, it is not possible to implement setting of the optical matrix switches so as to establish an optical path between the #1 input optical fiber and the #2 output optical fiber, or between the #2 input optical fiber and the #1 output optical fiber, even using the optical matrix switches through which any of the wavelengths from λ1 through λ4 passes, since a signal of the same wavelength as an already existing optical path is being outputted from the same output optical fiber.
On the other hand, as another method for implementing the establishment of optical paths between the input optical fibers and output optical fibers, there is a method as shown in FIGS. 32A through 32D, in which the optical paths between the input optical fibers and the output optical fibers are arranged. In detail, there is the method in which: optical paths which use the wavelength λ1 are established between the #1 input optical fiber and the #3 output optical fiber and between the #3 input optical fiber and the #1 output optical fiber; optical paths which use the wavelength λ1 are established between the #2 input optical fiber and the #5 output optical fiber and between the #5 input optical fiber and the #2 output optical fiber; optical paths which use the wavelength λ2 are established between the #2 input optical fiber and the #8 output optical fiber and between the #8 input optical fiber and the #2 output optical fiber; and optical paths which use the wavelength λ2 are established between the #1 input optical fiber and the #3 output optical fiber and between the #3 input optical fiber and the #1 output optical fiber.
In these circumstances, it is possible to utilize the wavelength λ3 or the wavelength λ4 for setting of the optical matrix switches so as to establish a further optical path between the #1 optical fiber and the #2 optical fiber, and, as compared with the previous case, it is possible to enhance the efficiency of utilization of the optical matrix switches.
In this manner, in order to utilize an optical cross connect device formed by combining small scale optical matrix switches efficiently, it is necessary to establish an optical path by planning a method of utilizing wavelengths so as to enhance efficiency.